Reflection in sphere becomes more distorted as subsurf increases?
Even if the Ico sphere has a nice distribution of triangles it isn't the best topology for normals. Worse is that it subdivides very bad since it is all triangles. The results gets worse since the frequency of the subdivision pinches increases. 

The UV sphere gives better result but you get pinching deformations at the poles since they are triangles.

To get the best possible result for subdivision use a subdivided cube and add a Cast Modifier (cast type "Sphere") to get it to be a sphere. This creates an all quad topology with only 8 3-edge poles.


To further improve the normals you can add an Edit Normals Modifier set to Radial and enable Auto Smooth in the Mesh properties. Now the normals will go straight out from the centre of the Sphere.